Adjustable gastric banding apparatus have provided an effective and substantially less invasive alternative to gastric bypass surgery and other conventional surgical weight loss procedures. Despite the positive outcomes of invasive weight loss procedures, such as gastric bypass surgery, it has been recognized that sustained weight loss can be achieved through a laparoscopically-placed gastric band, for example, the LAP-BAND® (Allergan, Inc., Irvine, Calif.) gastric band or the LAP-BAND AP® (Allergan, Inc., Irvine, Calif.) gastric band. Generally, gastric bands are placed about the fundus, or esophageal junction, of a patient's upper stomach forming a stoma that restricts food's passage into a lower portion of the stomach. When the stoma is of an appropriate size that is restricted by a gastric band, food held in the upper portion of the stomach may provide a feeling of satiety or fullness that discourages overeating. Unlike gastric bypass procedures, gastric band apparatus are reversible and require no permanent modification to the gastrointestinal tract. An example of a gastric banding system is disclosed in Roslin, et al., U.S. Patent Pub. No. 2006/0235448, the entire disclosure of which is incorporated herein by this specific reference.
Existing gastric bands periodically require adjustments to maintain an effective constriction about the fundus, to account for changes in the fundus tissue, reduction of fat or other factors causing movement and/or size change of the fundus. Some attempts have been made to allow for such adjustment of gastric bands. For example, hydraulic gastric bands utilize a fluid such as saline to fill an inflatable portion of the gastric band using a subcutaneous injection port. Adjustments to the amount of inflation may be made by injecting or extracting the fluid through the patient's skin into or out of the injection port, which then directs the fluid into or out of the inflatable portion of the gastric band. These types of adjustments may be undesirable because of the discomfort caused by the injections.
Further, adjustments by injections may not be immediately available when immediate adjustments may be desirable. For example, during normal operation of the gastric band, the band applies pressure to the outer surface of the fundus. But in some instances, the patient may swallow a bolus of food that is too large to pass through the constriction produced by the band. The result can be a painful experience which, if it persists, may require medical intervention to release the blockage.
Accordingly, it is desirable to develop a self-adjusting gastric band that will provide the needed pressure to the fundus to create the stoma and facilitate weight control, but that will also automatically self-adjust to account for changes in the fundus and/or to open up to allow a large bolus to pass through. It is further desirable to create an automatic, self-adjusting gastric band that does not require an electrical power source and/or external adjustments, to allow a large bolus to pass through, so that immediate relief from the discomfort created by a large bolus may be relieved. Moreover, it is desirable to develop a mechanically self-adjusting gastric band that does not require hydraulic adjustments through a subcutaneous injection port.